This invention relates to implantable medical devices. In particular, it relates to implantable medical devices having signal processing channels using sigma-delta analog-to-digital converters.
Implantable medical devices (IMD's) are used for a variety of monitoring and therapy delivery purposes. Many IMD's sense physiologic signals and provide outputs, either in the form of delivered therapy or in the form of monitored physiologic activity. For example, pacemakers and implantable cardioverter defibrillators (ICD) include electrodes (and in some cases other sensors) to sense cardiac activity. The sensed signals representing cardiac activity are processed in signal processing channels, and are used in the detection of cardiac arrhythmias and other conditions that require the delivery of therapy. The types of therapy that can be delivered include pacing pulses and cardioversion/defibrillation shocks delivered to the heart.
The signal processing of physiological signals, such as signals representing cardiac activity, has generally been performed by analog circuitry. Digital signal processing offers potential benefits over analog circuitry currently used in IMDs, but also poses challenges to implementation in IMDs. To achieve digital signal processing in an IMD, analog physiologic signals must be converted to digital form, through the use of analog-to-digital converters. One of the challenges presented in implementing digital signal processing channels in IMDs has been the amount of electrical energy consumed by the analog to digital conversion process. IMDs typically use batteries contained within the IMD housing as a sole source of electrical energy. The rate at which electrical energy from the battery is used affects battery life, and therefore the usable life of the IMD.